1. Field of the Invention
The present invention relates to a reference electrode used for measuring the concentration of various kinds of ions in a liquid by combining it with various kinds of ion electrodes, more specifically to a reference electrode for use at high pressure and comprising a liquid-junction contacting a liquid to be tested and which is at high pressure, a space which is open to said liquid-junction and housing an internal solution therein, and a further space which is open to the liquid to be tested for compensating for the pressure of the liquid to be tested.
2. Description of the Prior Art
It is a well-known practice, where a liquid to be tested is under pressure, for example the primary cooling water of a nuclear reactor, to introduce the liquid to be tested into an internal solution through a liquid-junction to reduce the concentration of said internal solution, whereby an electric potential is changed.
One of the disadvantages of such a practice is that pressure compensation must be carried out by holding the space for containing said internal solution under the same high pressure as that of the liquid to be tested. Various means for pressure compensation have been proposed and put into operation. A typical one has a construction as shown in FIG. 2.
Referring now to FIG. 2, this conventional reference electrode comprises a body 1, a cylindrical body 4 fixedly mounted in said body 1 and enclosing a space 3 for containing the internal solution therein, and a liquid-junction 5 formed in a portion of said cylindrical body 4 which projects out of said body 1. A space 6 is left between said cylindrical body 4 and said body 1 for receiving a liquid to be tested, the liquid to be tested being admitted into a pressure compensating space 7 within said body 4 through said space 6 and openings 4a in body 4. A piston 18 is slidably inserted in said cylindrical body 4, and an O-ring 19 is provided around said piston 18 and against the inside surface of said cylindrical body 4 and between said piston 18 and an internal electrode A, respectively extending through said piston 18 into said space 3, said space 3 containing an internal solution. The space 3 and space 7 are thus separated from each other by said piston 18.
Accordingly, when this reference electrode has the projecting portion of cylindrical body 4 inserted in the liquid to be tested which is at high pressure, for example by threading the threaded end 1a of body 1 into a threaded opening in a conduit for the liquid to be tested, the liquid to be tested is introduced into said space 7 through said space 6 and opening 4a for moving the piston 18 for holding the pressure inside said space 3 in which the internal solution is contained at the same high level as that of the liquid to be tested.
However, in this conventional reference electrode, since the pressure compensation is carried out by sliding said piston 18 relative to the body 1 and the cylindrical body 4, the liquid to be tested cannot be completely prevented from being introduced into said internal solution in the space 3 past the piston 18, thereby producing an error in the measurement made by electrode A. This occurs even though the O-rings 19 are provided. In addition, this conventional reference electrode has many other disadvantages. For example, the smooth sliding of said piston 18 is increasingly obstructed whereby it takes a long time for the pressure compensation if an effort for preventing said liquid to be tested from being introduced into said internal solution is made.